This invention relates to the testing of hearing protection devices.
Some industrial environments are very noisy due to hydraulic presses, grinding machines, and other industrial equipment. The noise from these machines can cause permanent hearing damage to employees if protection is not provided. Hearing conservation regulations, such as those promulgated by the Occupational Safety and Health Administration (OSHA), govern hearing protection for employees based on the number of decibels and the time of exposure. The decibel range is logarithmic from about 30 dB for virtually no sound, to about 130 dB for sound which is painful. An office, bank, or store might have a background noise level of about 40-55 dB, whereas a dance club might be about 100-120 dB.
To reduce the noise level in a high noise environment to an acceptable level, hearing protection devices (HPDs), such as muffs or ear plugs are used. HPDs are typically tested in a laboratory environment. According to one method, an artificial test head or dummy head, which has artificial flesh and artificial ear drums, is used. When testing a muff type protector, a microphone is positioned inside the head near the artificial ear drum and another microphone is positioned outside the muff. Typically, the noise attenuation test uses pink noise, an average of about 100 common industrial noises, as a noise source. The difference in sound levels received by the two microphones is calculated for each of a series of octaves or, sometimes, one third octaves. This difference is the attenuation of the HPD in each frequency range.
According to another method of testing, a person uses a muff or ear plugs, and noise is increased until he or she indicates that the noise is at a certain point, e.g., at the threshold of hearing. The person is separately tested with and without protection, and the two results are compared to determine the attenuation of the protection device.
These laboratory methods are not entirely adequate because they fail to consider what benefit people receive from the HPDs at an actual job site or factory. First, different industrial environments have much different noise patterns. A grinding machine and a hydraulic molding machine may have much different frequency characteristics. Some characteristics are regular and continuous, others are intermittent. Second, a muff is affected by various personal individual factors such as hair on the head, facial hair, eye glasses, and hard hats. Third, the wear and tear of the muff can affect how much noise is attenuated. Certain conditions of the muff vary as it ages, such as the wear of the lining, fatigue in the spring bands, and deterioration in the seals.
Accordingly, it is an object of the present invention to provide a hearing protection device evaluation apparatus which allows measurement in the field.
It is another object of the invention to provide a hearing protection device evaluation apparatus which is portable.
It is yet another object of the present invention to provide a hearing protection device evaluation apparatus which is easy to use by a test engineer.
It is still another object of the present invention to provide a hearing protection device evaluation apparatus which provides an easily readable and understandable indication of the noise attenuation.